Apparatus for manufacturing products from a thermoplastic mass

ABSTRACT

An apparatus for manufacturing products from material which is thermoplastically deformable, as from plastic, comprising: —a mold ( 2 ) with at least one mold cavity ( 3 ); —in the or each mold cavity ( 3 ) at least one slide ( 8 ); —movement means for moving each slide ( 8 ); —closing means for opening and closing the mold ( 2 ); —feed means for introducing, with the mold cavity ( 3 ) closed, said material in at least substantially plastic condition into the or each mold cavity; wherein the movement means ( 9 ) for moving the slide ( 3 ) are arranged for moving said slide forward at a relatively high speed relative to the movement speed of the mold parts upon opening and closing thereof, from a position at least partly retracted from the mold cavity, such that said material, as a result, is displaced in the mold cavity for obtaining the filling thereof, preferably at a speed high such that adiabatic heat development occurs in the or each mold cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 12/321,425, filed Jan. 21, 2009, now U.S. Pat. No. 7,891,970, whichis a divisional application of U.S. application Ser. No. 10/527,364,filed Apr. 27, 2005, now U.S. Pat. No. 7,504,059, which claims thebenefit of International Application No. PCT/NL2003/00630, filed on Sep.10, 2003, which claims priority to NL1021421, filed Sep. 10, 2002.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for manufacturing products from anat least thermoplastically deformable material. Such a method is known,for instance, as injection molding.

With known injection molding techniques, as a rule, the material to beformed such as plastic is heated in a plasticizing device to atemperature such that the material becomes virtually liquid, at leastplastic and low-viscous, whereupon the material is introduced under highpressure into a mold cavity of an injection molding mold. In this moldcavity, the material is distributed such that the mold cavity iscompletely filled, whereupon the material is allowed to cure by coolingdown. Thereupon, the product is taken out by opening the mold andejecting the product.

For such known injection molding techniques, a particularly high feedpressure is to be used, especially when thin-walled products are formed,in particular if the flow paths in the mold cavity closely approach themelt flow index (MFI) of the materials to be used. Therefore, the sameholds in particular when the flow paths in the mold cavity arerelatively long. It is clear that with plastics with a high viscosityand/or a low melt flow, these problems occur to a larger extent. As aresult, limitations are imposed on the minimum and maximum sizes ofproducts, in particular on lengths of flow paths, on passage widths ofsuch flow paths, on the duration of the injection molding cycles, on thematerials to be used and on the minimum wall thicknesses of products, inparticular of large, flat parts.

The use of compression molding is already known. Here, into a moldcavity of a partly open mold, an amount of plastic is introduced,required for forming a desired product in this mold cavity. After theplastic has been introduced into the mold cavity, the mold is closedfurther, so that the plastic is pushed away for filling the further moldcavity. Therefore, with such an apparatus, at the start of theintroduction of the plastic, the mold parts are to be held partly awayfrom each other, and only afterwards to be brought onto each otherrelatively slowly but with high pressure. The danger exists that then,the plastic is not uniformly distributed, so that, for instance, a partof the material can be pressed sideways from the mold cavity before themold cavity is completely closed. Also, the danger exists thatinsufficient or, conversely, too much plastic is introduced into themold cavity. In this latter case, skin formation will occur between themold halves and, moreover, it will not be possible to close the moldcompletely. This leads to irregularly formed products and, moreover, topollution of the mold. A further disadvantage of this apparatus is thatwhen materials are used with a low viscosity and/or with shallow moldhalves, the material flows from the mold cavity before the mold halvesare moved together, so that the earlier mentioned problems occur to aneven larger extent.

SUMMARY OF THE INVENTION

The object of the invention is to provide an apparatus of the typedescribed in the opening paragraph, wherein in a simple manner and withrelatively low closing pressures, products can be manufactured having atleast parts with a relatively limited wall thickness.

A further object of the invention is to provide an apparatus of the typedescribed in the opening paragraph, wherein different materials can beprocessed, in particular plastics, in particular also plastics with ahigh melt, i.e. plastics with a low viscosity in plastic state.

A still further object of the invention is to provide a method withwhich, in a relatively rapid and simple manner, products can bemanufactured, with relatively simple means, which products, moreover,can have relatively large, thin-walled surfaces, in particular productswith wall thicknesses which are relatively small and flow paths whichare relatively long, smaller or longer, respectively, than matching themelt flow index associated with the material from which the product ismanufactured.

The invention further contemplates providing an improved use of aninjection mold with a slide.

A number of these and many other objects are achieved with an apparatus,method and/or use according to the invention.

An apparatus according to the invention is characterized by a mold withat least one mold cavity; wherein in the or each mold cavity at leastone movable part, to be called slide, is provided; movement means formoving the slide; closing means for opening and closing the mold suchthat the mold cavity is released or closed, respectively; feed means forintroducing, with the mold cavity closed, said material in at leastsubstantially plastic condition into the mold cavity; wherein themovement means for moving the slide are arranged for moving said slideforward in the mold cavity at a relatively high speed relative to themovement speed of the mold parts upon their opening and closing, from aposition at least partly retracted from the mold cavity, such that, as aresult, said material is displaced in the mold cavity for obtaining thefilling thereof, said slide moving at a speed sufficiently high suchthat adiabatic heat development occurs in the mold cavity.

With an apparatus according to the invention, a thermoplastic materialsuch as a plastic, in particular a thermoplastic plastic, can beintroduced into a mold cavity while the mold as such is closed and theor each slide is in, or is being brought into, a retracted position atintroduction of the material, so that the volume of the mold cavity isrelatively large with respect to the volume of the product to beeventually formed. After the material has been introduced entirely or,preferably, substantially into the mold cavity, the or each slide can bemoved forcefully and, in particular, with speed into the mold cavity, atleast into the material introduced therein, so that this is pushed away.With it, a speed is developed such that, as a result of the movement ofthe or each slide, heat development occurs in the material. To that end,the movement means are designed such that the slide can move at thedesired high speed and with the desired accuracy.

Preferably, the movement means and the slide are designed such thatadiabatic heat development occurs, so that the temperature in thematerial rises above the melting temperature of the respective material.

In an advantageous embodiment, the closing means are included at leastpartly in or on the mold, preferably such that no press is required orthat a press without guide rod can suffice. Optionally, also, blockingmeans can be provided on the mold for holding the mold in closedcondition during introduction of the material and displacement of the oreach slide.

With an apparatus according to the invention, the mold can be heldclosed with relatively little closing pressure and the plastic can beintroduced, in comparison with a conventional injection moldingapparatus. By way of illustration: with conventional injection molding,feed pressures of between, for instance, 350 bars and 1000 bars or moreare used, with closing pressures of, for instance, 0.25 to 1.25 ton/cm²,depending on, in particular, the material used, the wall thickness andthe maximum flow path. With a method according to the invention, forcomparable products, a feed pressure of, for instance, between 0 and 200bars excess pressure can suffice, while relatively low pressures arepreferred, for instance of some tens of bars or less. In the Table, anoperating pressure of approximately 300 bar (operating pressure of thecylinders of the slides) is given, while the closing pressure can be,for instance, less than 0.2 ton/cm². With polypropylene, for instance, aclosing pressure of 0.025 to 0.1 ton/cm² instead of between 0.25 to 1.25ton/cm² can suffice.

Without wishing to be bound to any theory, this appears, in particular,to be the result of the insight that by temporarily increasing thevolume of the mold cavity, at least when introducing the larger part ofthe material such as the plastic into the mold cavity, the relationbetween the length of the flow paths and their passage, substantiallydetermined by the minimum wall thickness of the product to be formed,becomes more favorable, so that the material experiences relativelylittle counter pressure in the mold cavity, while the injection openingor openings are so small that upon movement of the slide or slides, thematerial is not pushed back through this opening or these openings.Moreover, then, the advantage appears to be achieved that due to thehigh speed of the or each slide, as a result of friction, so much heatis introduced into the material that solidification of the material, inparticular against the mold parts and in the flow front thereof, isundone so that the viscosity of the material is reduced again, while theremaining length of the flow paths for this flow front at the start ofthe movement of the or each slide has been considerably reduced relativeto the original length thereof. As a result, the material can bedistributed in the entire mold cavity with less pressure. As the mold isthen closed, in a simple manner, the material is prevented from flowingaway prematurely.

Surprisingly, it has appeared that then, a high feed rate isparticularly advantageous. For instance, a feed rate can be used ofbetween 100 and 2000 mm/s, more in particular of between 500 and 1000mm/s. This rate is selected depending on the solidification rate of theplastic used, while it holds that the more quickly the plasticsolidifies, the higher the feed rate is chosen to be. Moreover, the rateis selected depending on the mold geometry and, in particular, thede-aeration, such that undesired pressure increase in the mold cavity bycompression of air is prevented.

With a mold according to the invention, in the movement means,preferably, wedge-shaped elements are used which, viewed from the moldcavity, are moved behind the or a slide, such that the respective slideis moved as a result of the wedge-shape. In particular, then, for eachslide at least two wedge-shaped elements are used which are pushed inopposite directions behind the slide so that a symmetrical load isobtained. Through the use of such wedge-shaped elements a favorabledistribution of forces is obtained and the slides can be moved over thedesired distance with relatively little force.

In a mold according to the invention, preferably, at least one slide isprovided at the location where the smallest wall thickness is providedin a product and/or at the location where the flow paths have thegreatest length and/or at the location where the flow paths have thegreatest complexity. By retracting the slides in those parts uponinjection of the plastic, at least moving them partly from the moldcavity, additional space is created for allowing the plastic to passexactly at the location where the plastic experiences the mostresistance or at the location where excessive pressures would benecessary for allowing the plastic to pass. This holds in particular atthe location where already some solidification of the plastic occurs.The adiabatic heat introduced later causes the plastic to flow further,while, moreover, the displacement of the slide effects the furthermovement of the plastic. Furthermore, with such a mold, relativelylarge, thin-walled product parts can be obtained with wall thicknessesthat cannot be obtained with conventional injection molding technique.

Slides in a mold according to the invention can have a frontal surfacewhich is relatively large in relation to the projected surface of theproduct. Herein, projected surface is understood to include the surfaceof the product projected on a plane at right angles to the closingdirection of the mold. For instance, the frontal surface of the slidecan be more than 20% of this projected surface. Surfaces of more than50%, for instance of 75%, 85% or 95% or more are possible. With this,the advantage is achieved that in a major part of the mold cavity, thespace for primary flow of the material to be formed is increased, while,eventually, thin-walled products can be manufactured. As a result ofthis as well, the feed pressure and the closing pressure can be kepteven lower.

The invention further relates to a method for forming products, wherein,in a mold cavity, an amount of plastic is introduced in substantiallyplastic condition, whereupon at least one movable element to be called aslide is moved at least partly into the respective mold cavity whilecompressing and/or displacing at least a part of the plastic, while thespeed of movement of the at least one slide is so high that adiabaticheat development occurs in the plastic, such that the plastic becomesmore liquid, at least its viscosity is decreased.

With such a method, in a rapid and simple manner, plastic products canbe manufactured, while low pressures can be used for injection of theplastic as well as closure of the mold. As low injection pressures canbe used, the advantage can be achieved that no undesired chemical ormechanical changes occur in the plastic, in particular separation in thedifferent monomers or polymers, while the closing pressure can be keptlow, which is advantageous from a point of view of costs. The fact isthat for that purpose, simpler apparatuses are suitable, while moreover,the mechanical load is lower and less wear will occur. A furtheradvantage thereof is that, in principle, less space is required for suchan apparatus.

With a method according to the invention, plastic is introduced into themold cavity while the or each slide is retracted therefrom at leastpartly or is pushed back upon injection, so that additional flow spaceis obtained. This has already been discussed hereinabove with referenceto an apparatus according to the invention. Thus, the resistance theplastic experiences is reduced, so that the injection pressure can bekept low, for instance largely below the standard injection pressure forconventional injection molding of a similar type of product from thesame plastic. Such standard pressures can be read from standard tablesand, as a rule, are dependent on the plastic and the manner ofinjection, the projected surface of the products to be formed jointlyand the wall thicknesses. As a result thereof, the closing pressure canalso be kept low in relation to conventional injection molding, readablefrom the same or comparable tables on the basis of substantially thesame quantities. This is directly clear to the skilled person.

With a method according to the invention, after the mold cavity has beenat least substantially filled, the or each slide is moved rapidly intothe mold cavity, such that the eventual product shape is obtained. Thespeed of the or each slide is then set such that adiabatic heatdevelopment occurs in the plastic, so that the temperature is increasedagain to approximately the melting temperature of the plastic. As aresult, partially solidified material will become liquid again and bepushed further into the mold cavity, while, furthermore, the remainingflow paths are relatively short so that relatively thin product partscan be formed.

With a method according to the invention, the rate of movement of the oreach slide is preferably high, such that the complete movement of theslides is carried out in a fraction of the cycle time of a productcycle, for instance in less than 10%, more in particular in less than 3%of the cycle time, preferably less than some tenths or hundredths ofseconds, more in particular microseconds. As stated, this rate is setsuch that the desired temperature increase occurs, while the plasticproperties are prevented from being adversely thermally influenced.

With a method according to the invention, the distance between the endof the or each slide, leading in the direction of movement and facingthe mold cavity in the retracted position, at least partly moved fromthe mold cavity, and an oppositely located wall part of the mold cavityor slide is set depending on at least the melt of the plastic, i.e. theviscosity of the plastic upon injection. Surprisingly, it has appearedthat, preferably, at a higher melt, i.e. a higher viscosity, thedistance is to be slightly greater than with a lower melt. Withoutwishing to be bound to any theory, this appears to be the result of thefact that the plastic with the higher melt will solidify sooner and theplastic with the lower melt has a more disadvantageous MFI. For anyplastic/mold combination, the optimal distance can be determined in asimple manner by way of experiments.

The invention further relates to a use of a mold for forming products,and a product.

BRIEF DESCRIPTION OF THE DRAWINGS

In clarification of the invention, exemplary embodiments of anapparatus, method, use and product will be described with reference tothe drawing. In the drawing:

FIG. 1 shows, in partly cross-sectional side view, an apparatusaccording to the invention, with partly opened mold;

FIG. 2 shows, in partly cross-sectional side view, an apparatusaccording to the invention, with a closed mold and retracted slide;

FIG. 3 shows, in partly cross-sectional side view, an apparatusaccording to the invention, with a closed mold and forwardly movedslide;

FIG. 4 shows, in partly cross-sectional side view, an alternativeembodiment of an apparatus according to the invention;

FIG. 5 is a graph showing the temperature in the plastic in a moldaccording to the invention during an injection molding cycle, plottedagainst time; and

FIG. 6 shows a depiction of a CD-box manufactured according to theinvention, photographically recorded using colorant.

FIG. 7 shows, in partly cross-sectional side view, an apparatusaccording to the invention with two mold cavities, each having a slide;

FIG. 8 shows, in partly cross-sectional side view, an alternativeembodiment of an apparatus according to the invention with two moldcavities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this description, identical or corresponding parts have identical orcorresponding reference numerals. The embodiments shown are only givenby way of example and should not be taken as being limitative in anyway.

FIG. 1 shows, in cross-sectional side view, an apparatus 1 according tothe invention, provided with a mold 2 with a mold cavity 3 therein. Themold comprises a first, moveable part 4 and a second, complementary part5, fixedly arranged. The moveable part 4 is guided by suitable guides,which are not shown but can, for instance, be sliding pins, rails, guiderods or a press or the like and which are directly clear to the skilledperson. The moveable part is moveable with the aid of devices suitableto that end, represented in FIGS. 1-3 as piston-cylinder assemblies 7.It is clear that this may be any suitable device, for instance also asimple press, screw means such as spindles as shown in FIG. 4, linksystems or the like. These can be of relatively light design as they areonly meant for moving the part 5, virtually not for absorbing tensile orpressure forces in the further cycle.

In the fixed part 5, a slide 8 is provided, moveable in the direction Sbetween a retracted position shown in FIGS. 1 and 2, and an extendedposition shown in FIG. 3. For moving the slide 8, two wedges 9 areprovided, to be called wedge-shaped elements, which are moveable in adirection P with the aid of piston-cylinder assemblies 10 which are, forinstance, hydraulically driven from a central control unit 11. Thewedges 9 move in the direction P approximately at right angles to thedirection S. At the underside, the slide 8 is provided with two surfaces12 inclining in opposite directions, complementary to the top surfacesof the wedges 9, such that if the wedges 9 are moved inwards, towardseach other, the slide 8 is moved upwards (directions viewed in the planeof the drawing) towards the extended position and vice versa.

An inflow opening 14 terminates in the mold cavity 3 and is connected toan injection device 15, for instance a plasticizing device and,optionally, a pressing device. On both parts 4, 5 of the mold 2, flanges16 are provided which, with the aid of blocking means 17, can be pressedand held onto each other, for keeping the mold closed. To that end, inthe embodiment shown, the blocking means comprise brackets 18 which aremoveable with the aid of piston-cylinder assemblies 19 and can be pushedover the flanges 16. In this way, simply, the desired closing pressurecan be obtained and maintained.

As an example, on the top surface 20 of the slide 8, two ribs 21 areprovided extending over the entire width of the slide 8, at right anglesto the plane of drawing. The distance D between the end 22 of the ribsleading in the direction of movement, and the oppositely located surface23 of the mold cavity is set with the slide 8 retracted, depending onthe desired product wall thickness and the plastic to be used, while thedistance is set to be larger according as the melt of the plastic ishigher and/or the melting temperature of the plastic is lower.

With an apparatus according to FIGS. 1-3, a product can be formed, forinstance a sheet with two hinges from thermoplast such as polypropyleneor polyethylene, as follows.

The mold 2 is closed from the position shown in FIG. 1, as shown in FIG.2. The distance D is then set at a suitable value, such that the spacein the mold cavity 3 is relatively great. Through the inflow opening 14,under relatively low pressure, plastic is introduced into the moldcavity, for instance at a pressure of between 1 and 10 bars excesspressure. The filling pressure is selected such that a desired, shortfeed time is achieved without the material properties of the plasticbeing adversely affected and without undesirably high pressure occurringin the mold cavity. Then, at a relatively high speed, the slide 8 ismoved forward, in the direction of the extended position, a shown inFIG. 3, by moving the wedges 9. Here, the speed is selected dependent onthe desired adiabatic heat development which should be such that thetemperature of the plastic is at least substantially increased toapproximately the melting temperature thereof. Plastic that is,possibly, slightly solidified becomes liquid again and can be forcedfurther into the mold so that a complete filling of the mold cavity isobtained while the product can have wall thicknesses which are, in fact,too small for the melt flow index of the respective plastic/productcombination. Optionally, after removing the slide, some hold pressurecan still be given with the aid of the injection device 15, so thatundesired stresses can be pressed from the product.

After that, the mold can be opened again and the product can be takenout.

Preferably, the rate of movement of the or each slide is high such thatthe time of movement of the slide between the retracted and the extendedposition is relatively short with regard to the cycle time for themanufacture of a product, for instance between 0 and 10% of that time,also depending on the desired adiabatic heating. This can be determinedby way of an experiment for each plastic-product combination or becalculated with the aid of standard tables regarding plastics, theproduct properties such as dimensions and flow paths, the friction whichwill occur when moving the slide and the heat capacity and melttemperature of the plastic.

In FIG. 4, an alternative embodiment of an apparatus according to theinvention is shown, wherein screw spindles 25 with nut blocks 26 areused for opening and closing the mold 2. These can be wholly or partlyincluded in the mold 2. In this embodiment, the plastic is introducedvia a side inflow opening 14 and a slide 8 is provided on both sides ofthe mold cavity 3. In this embodiment, they can be moved independentlyof each other but it is preferred that they be moved in coupledrelation, so that a symmetrical load occurs in the mold 2.

By way of illustration, an embodiment of a mold and method according tothe invention will be described. As a product example, a plastic file istaken. In Table 1, the data of the injection molding machine areincluded, in Table 2 the mold data, in Table 3 the product dimensions,in Table 4 the data about the slides or pressure plate and in Table 5data involving the operation parameters. In Table 6, the pressures andspeeds used during an injection molding cycle are given. Thereupon, inFIG. 5, the temperature in the plastic in a mold according to theinvention during an injection molding cycle is given, plotted againsttime.

TABLE 1 Machine Data Machine Stork SX 3000-2150 Machine Number X 2936Year of Construction  2000 Main Feed 400 V 50 Hz Main Current 354 AControl Voltage 24 V Max Oil Pressure 210 bar Max Air Pressure 8 barWeight Closing Force 8700 kg Weight Injection Force 5000 kg Screwdiameter 65 mm

TABLE 2 Mold Data Length 1050 mm  Width 455 mm Height 495 mm Number ofCavities 1

TABLE 3 Product Size Length 655 mm Width 320 mm Thickness  1.7 mm

TABLE 4 Pressure Plate Data Cylinder Stroke 50 mm Cylinder Diameter 80mm Operating Pressure 300 bar Wedge Angle 4°

TABLE 5 Parameters Mold Temperature  50° Temperature at Introduction245° Dosing 128 mm Shot Weight 295 gram Impact of the Pressure Plate 80mm Decompression 10 mm Closing Force 150 ton Hold Pressure 25 bar Thrust20 bar Speed of Impact 0.4 S

TABLE 6 Cycle Time Sub Time At Time Total Time Closing 0.750 S T = 0.000S  0.750 S Injection 0.171 S 0.750 S  0.921 S Impact Pressure Plate0.400 S 0.857 S  1.257 S Cooling 12.000 S  1.257 S 13.257 S Opening1.000 S 13.257 S 14.257 S Handling 5.000 S 14.257 S 19.257 S

With a method according to the invention, at a time 0, with the moldclosed, an amount of plastic was introduced into the mold cavity,sufficient for manufacturing an end product, in this case a file. In0.1706 sec, a shot weight of 128 grams of PP was introduced into themold cavity. The mold cavity comprised a slide with a frontal surface ofapproximately 200,000 mm², which was moved over a distance of 1.8 mm.The plastic was introduced, at a temperature of approximately 245° C. ata speed of 750 mm/s, without pressure, at a mold temperature ofapproximately 50° C., and was cooled down in a first phase toapproximately 230° C. At the time T1, after approximately 0.107 seconds,the slide was set in motion, which slide was moved completely forwardsin approximately 0.4 sec, while the temperature in the mold rose to justbelow the temperature at which the plastic will decompose. From the timeT2, at which the slide was completely moved forward and was held in thatposition, the plastic was allowed to cool down to a temperature wellbelow the melting temperature, close to room temperature, for instance45 to 55° C. This cooling down was done in approximately 12 seconds.Apart from two living hinges, the product thickness on the covers andthe back was on average 1.7 mm by, viewed in frontal surface, 655 mm by320 mm. During cooling down, the application of hold pressure was notnecessary, as a result of the fact that no shrinkage needed to beabsorbed. The product appears to be free of stress, so that a highform-stability is obtained.

As a result of the high speed of the slide, kinetic speed is convertedto heat, while, moreover, friction between the plastic and the mold aswell as in the plastic itself and the compression leads to adiabaticheat development. Until approximately the moment T2 the slide iscompletely moved forward, the plastic in the mold is kept in motion and,furthermore, kept above the melting temperature, so that solidificationis prevented and the flow behavior of the plastic is positivelyinfluenced. As a result, a complete filling of the mold cavity isobtained with limited closing force and filling pressure.

The mold was moved with wedges with a wedge angle of approximately 4°.

With a method according to the invention as described herein, the slideis already moved to the extended position while the plastic is beinginjected into the mold cavity. This also contributes to the plasticbeing kept in motion.

In FIG. 6, a photographic depiction is given of a CD-box manufacturedwith a method according to the invention. Here, the flow pattern of theplastic is clearly visible. FIG. 6 is to be explained as follows.

With conventional injections, a tangle of lines would be visible. Withconventional injecting, these lines are caused by plastic being suppliedunder pressure. A very dark, confused pattern becomes visible andindicates the presence of stresses in the material. Conversely, in thispicture, a particularly quiet image presents itself with attractive,long threaded light patterns. A slight hold pressure causes the two darkspots around the points of injection. In itself, this hold pressure isnot necessary but hold pressure can be advantageous for furtherimproving the product, in particular the flatness thereof. The slightlydarker spots near the center are the result of this hold pressure which,clearly, has remained particularly limited.

The invention is not limited in any manner to the embodimentsrepresented in the drawing and the description. Many variations thereonare possible within the framework of the invention as outlined by theclaims. For instance, a mold 2 according to the invention can compriseseveral mold cavities, while the or each mold cavity can be providedwith one or more slides, as shown in FIGS. 7 and 8. The slides can bedriven in different manners, for instance directly, as shown in FIG. 7,instead of by the wedges, as shown in FIG. 8, and with the aid ofdifferent means, for instance electrically. Also, the slides can move indifferent directions, for instance approximately at right angles to thedirection of movement of the mold parts, or be pivoted for reducing thespace in the mold cavity.

These and many comparable adaptations are possible within the frameworkof the invention as outlined by the claims.

Although the illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the invention.

1. An apparatus for manufacturing products from a thermoplasticallydeformable plastic material, the apparatus comprising: a mold havingfirst and second mold parts defining at least one mold cavity; a slidemovably disposed within the at least one mold cavity of the mold, saidslide being movable in a forward direction from a first position atleast partly retracted within the mold cavity to a second forwardposition, wherein said mold cavity defines a first volume when saidslide is in said first position, and wherein said mold cavity defines asecond volume when said slide is in said second forward position, saidfirst volume being greater than said second volume; movement means formoving the slide; closing means for moving the first and second moldparts together and apart, thereby opening and closing the mold such thatthe mold cavity is released or closed, respectively; feed means forintroducing, with the mold cavity closed, said material in at leastsubstantially plastic condition into the mold cavity, said feed meansincluding an injection inlet disposed opposite said slide in saidforward direction; and a central control unit for controlling saidmovement means and said closing means, wherein the movement means formoving the slide are arranged for moving said slide in the forwarddirection in the mold cavity toward said injection inlet from a positionat least partly retracted within the mold cavity such that said materialis displaced in the mold cavity for obtaining the filling thereof.
 2. Anapparatus according to claim 1, wherein the closing means are at leastsubstantially included in the mold.
 3. An apparatus according to claim2, wherein the closing means further comprise blocking means for holdingthe mold in closed position.
 4. An apparatus according to claim 1,wherein the movement means comprise cooperating elements, at least oneelement of which is at least partly wedge-shaped, the arrangement beingsuch that upon movement of one of the elements in a first direction, theslide connected thereto is moved in a second direction.
 5. An apparatusaccording to claim 1, wherein the mold cavity comprises at least oneforming part for forming a product part, wherein the slide is providedin or adjacent said forming part and which has a direction of movementsubstantially parallel to a wall thickness of said product part, while,with the slide in the first, at least partly retracted position saidforming part defines a first passage, said first passage having across-section larger than a cross-section of said product part, and inthe second, forward position, defines a second passage which correspondsto the cross section of the product part to be formed in said productforming part.
 6. An apparatus according to claim 5, wherein the secondpassage, with the slide in the second position, is at least partlysmaller than is necessary for the plastic material to flow past saidsecond passage while, with the slide in the first position, the firstpassage is greater than is necessary for the plastic material to flowpast said first passage.
 7. An apparatus according to claim 1, whereinthe feed means are arranged for introducing the material into the moldat a pressure lower than a required injection pressure when using a moldwithout slides for forming a same product from the same material.
 8. Anapparatus according to claim 1, wherein the slide, viewed in directionof movement, has a frontal surface, said frontal surface having asurface area greater than 25% of the projected surface of the moldcavity viewed in said direction of movement.
 9. An apparatus accordingto claim 8, wherein said frontal surface is more than 50% of saidprojected surface.
 10. An apparatus according to claim 9, wherein saidfrontal surface is more than 75% of said projected surface.
 11. Anapparatus according to claim 10, wherein said frontal surface is morethan 85% of said projected surface.
 12. An apparatus according to claim11, wherein said frontal surface is between 90% and 100% of saidprojected surface.
 13. An apparatus according to claim 1, wherein saidsecond volume of said mold cavity is substantially equal to the volumeof the product to be formed in said mold.
 14. An apparatus according toclaim 1, wherein said movement means comprises a piston-cylinderassembly hydraulically driven from said central control unit fordirectly driving said slide.
 15. An apparatus according to claim 1,wherein said slide is driven electrically.
 16. An apparatus according toclaim 1, wherein said slide is disposed at a location within said moldcavity of said mold where the smallest wall thickness is provided in aproduct and/or at the location where the mold cavity defines flow pathshaving the greatest length.
 17. An apparatus according to claim 1,wherein said slide is disposed within said mold cavity of said mold suchthat said slide is free to be pushed back toward said first position bysaid material being introduced into said mold cavity by said feed means.18. An apparatus according to claim 1, wherein said slide is providedwith a rib on a surface facing said mold cavity for forming a narrowingportion in the product.
 19. An apparatus according to claim 1, whereinsaid central control unit is adapted to start movement of said slidedirectly prior to completing the filling of said material into said moldcavity.
 20. An apparatus according to claim 1, wherein said mold definesa plurality of mold cavities, each of said mold cavities having a slidemovably disposed therein and being movable in a forward direction from afirst position at least partly retracted within the mold cavity to asecond forward position, wherein said mold cavity defines a first volumewhen said slide is in said first position, and wherein said mold cavitydefines a second volume when said slide is in said second forwardposition, said first volume being greater than said second volume.